An officer who joined Bokuto Station in the first season, Aoi is a trans woman whose biological sex is revealed after her appearance. While still identifying as male, she had cross dressed to go undercover as a decoy to catch a serial rapist in the vice unit and, in the process, “went native" - effectively coming to identify as female. Now, Aoi is more feminine in appearance and personality than any of the women in the station. In the second series, Aoi states on several occasions that "my body is male, but my heart is female". This sentiment is echoed and supported by Aoi's coworkers, who act and react as though Aoi is a woman, despite knowledge to the contrary. Aoi's romantic gender preferences are often speculated on by the Bokutou police, but in the end it is discovered that Aoi prefers men. In one case, a very famous actor (Mr. Kitakoji) proposed to her not knowing she was transgender, but was rejected (though Aoi was clearly attracted to him), and in fact this is the only time Aoi is seen wearing male clothing. In a second series episode, Aoi has become romantically involved with a man via the Internet, and is torn about meeting this man and revealing her secret.

Before entering the force, Aoi was an accomplished basketball player who had many female admirers due to her ability to outsmart her opponent and score good shots from critical positions. One of them had even accepted Aoi's new identity as a female. In the 2nd season, Aoi's hair color was changed from brown to black. It was shown that Aoi had chosen to be female after undergoing a sting operation with her ex-superior Udamura Kumanosuke.

In the original manga, Aoi's chosen sport is shown to be golf rather than basketball; she shows her prowess with a club in the section of the manga translated by Dark Horse.